#include <bits/stdc++.h>
using namespace std;
int f[20];
int main(){ 
    int n;
    cin >> n;
    f[1] = 1;
    f[2] = 2;
    for (int i = 3 ; i<= n; i++){
    	f[i] = f[i-1] +f[i-2];
	}
	cout << f[n];
    return 0;
}